If a product you are using in an upsell is showing up as having inventory issues, follow these steps to fix the problem:
- From "Shopify Admin", select Products.
- Select Inventory.
- Find the product that you are having difficulty with.
- On the far right, next to the product select add or set.
- add - adds an amount of stock to the inventory total.
- set - sets the total amount of inventory.
- Enter the amount of stock to add or the total number of stock available, depending on what you selected in step 4.
- Select Save.